To meet the demand for wireless data traffic having increased since deployment of 4th generation (4G) communication systems, efforts have been made to develop an improved 5th generation (5G) or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called a ‘Beyond 4G Network’ or a ‘Post Long Term Evolution (LTE) System’. The 5G communication system is considered to be implemented in higher frequency (mmWave) bands, e.g., 28 GHz or 60 GHz bands, so as to accomplish higher data rates. To decrease propagation loss of the radio waves and increase the transmission distance, the beamforming, massive multiple-input multiple-output (MIMO), Full Dimensional MIMO (FD-MIMO), array antenna, an analog beam forming, large scale antenna techniques are discussed in 5G communication systems.
In addition, in 5G communication systems, development for system network improvement is under way based on advanced small cells, cloud Radio Access Networks (RANs), ultra-dense networks, device-to-device (D2D) communication, wireless backhaul, moving network, cooperative communication, Coordinated Multi-Points (CoMP), reception-end interference cancellation and the like.
In the 5G system, Hybrid frequency shift keying (FSK) and quadrature amplitude modulation (FQAM) and sliding window superposition coding (SWSC) as an advanced coding modulation (ACM), and filter bank multi carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA) as an advanced access technology have been developed.
Accompanying with rapid developments of information industry, particularly increasing requirements coming from mobile Internet and internet of things (IoT), unprecedented challenges have been brought to future mobile communication technologies. For example, based on the report International Telecommunications Union-Radio Communications sector (ITU-R) M.[IMT.BEYOND 2020.TRAFFIC] of ITU, it can be predicted that by 2020, mobile traffic will grow nearly 1000 times compared with year 2010 (fourth generation mobile communication technology (4G) era), number of connected user equipment (UE) will be more than 17 billion. With massive IoT devices gradually penetrate into the mobile communication network, number of connected UEs may be more amazing. In response to this unprecedented challenge, communications industry and academia have launched a wide range of 5G research, for 2020s. At present, the report ITU-R M.[IMT.VISION] made by ITU has discussed framework and overall objectives of future 5G, and has provided a detailed description for demand outlook, application scenario and each important performance index. In response to new demands in 5G, the report ITU-R M.[IMT.FUTURE TECHNOLOGY TRENDS] made by ITU provides information about technology tendency of 5G, which aims to solve significant problems, such as significant improvement of system throughput, consistent user experience, expansibility, so as to support IoT, delay, energy efficiency, costs, network flexibility, support of emerging services, and flexible spectrum usage, and so on.
To be faced with more diverse service scenarios of 5G, flexible multiple access technologies are needed to support different scenarios and service requirements. For example, in the face of various service scenarios with massive connections, how to access more users with limited resources becomes a core problem needing to be solved by 5G multiple access technologies. Current 4G LTE network mainly adopts an Orthogonal Frequency Division Multiplexing (OFDM)-based multiple access technologies. However, it is obvious that current orthogonal-based access mode is difficult to meet the following requirements for 5G: spectral efficiency is increased by 5 to 15 times, and user access number per square kilometer area may reach one million. By reusing the same resources with multiple users, supported number of user connections may be greatly improved by Non-Orthogonal Multiple Access (NOMA) technologies. Since users have more chances to access a network, the overall throughput and spectrum efficiency of the network may be improved. In addition, in the face of massive Machine Type Communication (mMTC) scenarios, take into account of cost and realization complexity of a terminal, multiple access technologies with more simple operation and process are necessary to be used. In the face of low-latency or low-power service scenarios, when adopting NOMA technologies, access requirements of massive users may be better met. However, when adopting access modes of non-orthogonal multiple access resources, severe interference may be generated among each cell, particularly in a case where no individualized processing has been performed to multiple access resources employed by adjacent cells, under the circumstances that two adjacent cells use the same multiple access resources, and transmit signals with the same frequency band. Meanwhile, when adopting NOMA, from one aspect, number of served users may be improved; from another aspect, interference in a system environment may also be increased, e.g., interference level generated by users of an adjacent cell to current cell may be increased significantly.
At present, the NOMA technologies under research mainly include: Multiple User Shared Access (MUSA), NOMA, Pattern Division Multiple Access (PDMA), Sparse Code Multiple Access (SCMA), Interleave Division Multiple Access (IDMA), and so on. MUSA distinguishes users with code word. SCMA distinguishes users with codebook. NOMA distinguishes users with power. PDMA distinguishes users with different characteristic patterns. IDMA distinguishes users with interleaved sequence.
When applying current NOMA (SCMA, IDMA and so on) to a practical cellular communication system, number of users served simultaneously in a cell may be greatly improved. The problem brought at the same time is as follows. Accompanying with increasing number of users served in a cell, inter-cell interferences may also be significantly increased. Subsequently, Quality of Service (QoS) obtained by users in the cell, particularly QoS of users at the cell edge, may be affected seriously. Current network does not process the following problem. After applying NOMA, more users have been accessed, while inter-cell interferences have been increased.